Throughout this application, for convenience the invention is for the most part described as being used to cure the adhesive of flocked material. However, the invention is equally applicable to other elongated particles, such as those used in sandpaper. In the well established methods of making flocked material and also materials such as sandpaper, in which elongated particles are deposited on a substrate and secured thereto by an adhesive, the latter is first coated with the adhesive. Thereafter, by mechanical or electrostatic means the flock fibers are deposited on the substrate, each fiber standing on end thereon, the ends of the fibers being embedded in the uncured adhesive. As a result, the flock fibers or particles are attached only temporarily (prior to the setting of the adhesive) to the substrate, and the particular adhesive used must be then cured or set. The curing operation is commonly done in large heated ovens in which the substrate with its flocking is looped back and forth until it finally emerges at the exit end with the adhesive in a cured or polymerized condition.
Such treatments are relatively inefficient, are slow, and require large amounts of energy. As an example of the latter, a typical curing oven may be as much as 30 to 90 feet long, and typically will use six million BTU's of heat per hour during the passage of the material therethrough, due to the high water content where water-based adhesives are used. Where solvent-type adhesives are used, problems of pollution, flammability etc. arise. (This invention makes possible the use of monomers as adhesives which are polymerized by electron beam radiation.)
For tactile substrates, the temperature within the curing oven in which the material is treated varies between 240.degree. F. and 325.degree. F., but the temperature for thermoplastic substrates such as vinyl and styrene are generally half of the above temperatures.
Temperatures greater than 175.degree. may result in distortion, wrinkling, or have other deleterious effects on heat-sensitive materials being treated. As a result, for such heat-sensitive materials, the curing operation is slow and limits production. If, for example, a vinyl substrate of the order of a few thousandths of an inch in thickness is flocked by conventional methods and then subjected to the heat of a curing oven, the vinyl substrate tends to wrinkle during the curing of the adhesive. The resultant material is generally not suitable for sale, and consequently it has been held to be unfeasible to flock such materials.
In respect to the time of curing, the normal traversal of flock material through an oven may take as long as 20 minutes or longer, due to the low temperatures used. The latter figure is only by way of illustrative example.
In addition, if a defect in the cured flocked material is detected, it oftentimes is only after it emerges from the exit of the oven. Since it is not known how far back in the curing oven the defect occurs, several hundred feet of flocked material are generally wasted before the process can be properly continued.
Still another problem with the conventional adhesive-curing operations is the production down-time necessary for cleaning the ovens.